Golf ball

ABSTRACT

An object of the present invention is to provide a golf ball having excellent approach spin performance under a dry condition and excellent approach spin performance under a condition that there is grass between the golf ball and the club face. The present invention provides a golf ball comprising a golf ball body and a paint film formed on a surface of the golf ball body, wherein the paint film is composed of at least one layer, and an outermost paint film layer located at the outermost layer of the golf ball contains, as a base resin, a polyurethane obtained by a reaction between (A) a polyisocyanate composition and (B) a polyol composition, (B) the polyol composition contains a urethane polyol as a polyol component, and the outermost paint film layer has a dynamic friction coefficient of from 0.65 to 1.2 measured with a dynamic friction tester under specific conditions.

FIELD OF THE INVENTION

The present invention relates to a golf ball comprising a paint film.

DESCRIPTION OF THE RELATED ART

A paint film is formed on a surface of a golf ball body. Conventionally,it has been proposed that the performance of the golf ball has beenimproved by improving the paint film and controlling the frictioncoefficient of the golf ball.

For example, JP 2006-75209 A discloses a golf ball comprising a golfball body and a paint layer covering a surface of the golf ball body,wherein a resin component constituting the paint layer is a productcured by a polyamide curing agent, and the golf ball has a staticfriction coefficient of 0.22 or less.

JP 2013-176530 A discloses a golf ball comprising a golf ball body and apaint film formed on a surface of the golf ball body, wherein the golfball has a friction coefficient of 0.35 or more and 0.60 or lesscalculated using a contact force tester.

SUMMARY OF THE INVENTION

However, the conventional golf balls do not necessarily havesatisfactory spin performance on approach shots, and there is still roomfor improvement. In addition, in the conventional technologies, the spinperformance on approach shots under a condition that there is grassbetween the golf ball and the club face was not studied.

The present invention has been made in view of the abovementionedcircumstances, and an object of the present invention is to provide agolf ball having excellent spin performance on approach shots under adry condition and excellent spin performance on approach shots under acondition that there is grass between the golf ball and the club face.

The present invention that has solved the above problems provides a golfball comprising a golf ball body and a paint film formed on a surface ofthe golf ball body, wherein the paint film is composed of at least onelayer, and an outermost paint film layer located at the outermost layerof the golf ball contains, as a base resin, a polyurethane obtained by areaction between (A) a polyisocyanate composition and (B) a polyolcomposition, (B) the polyol composition contains a urethane polyol as apolyol component, and the outermost paint film layer has a dynamicfriction coefficient of from 0.65 to 1.2 measured with a dynamicfriction tester under following conditions:

<Measurement Conditions>

moving speed: 2 mm/s

load: 1.96 N

measuring item: dynamic friction average value in a moving distance offrom 2 mm to 10 mm.

In the golf ball according to the present invention, the base resin ofthe outermost paint film layer contains a polyurethane having a urethanepolyol as a polyol component, and the dynamic friction coefficient ofthe outermost paint film layer is controlled in a range of from 0.65 to1.2. By such the configuration, the obtained golf ball is excellent notonly in the approach spin performance under a dry condition but also inthe approach spin performance under a condition that there is grassbetween the golf ball and the club face.

According to the present invention, a golf ball having excellent spinperformance on approach shots under a dry condition and excellent spinperformance on approach shots under the condition that there is grassbetween the golf ball and the club face is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a partially cutaway cross-sectional view showing a golfball according to one embodiment of the present invention.

DESCRIPTION OF THE PREFERABLE EMBODIMENT

The present invention provides a golf ball comprising a golf ball bodyand a paint film formed on a surface of the golf ball body, wherein thepaint film is composed of at least one layer, and an outermost paintfilm layer located at the outermost layer of the golf ball contains, asa base resin, a polyurethane obtained by a reaction between (A) apolyisocyanate composition and (B) a polyol composition, (B) the polyolcomposition contains a urethane polyol as a polyol component, and theoutermost paint film layer has a dynamic friction coefficient of from0.65 to 1.2 measured with a dynamic friction tester under specificconditions.

(Paint Film)

The paint film may have either a single layered structure or a multiplelayered structure. The outermost paint film layer located at theoutermost layer of the golf ball contains a polyurethane as a baseresin, wherein the polyurethane includes (A) a polyisocyanatecomposition and (B) a polyol composition as constituent components. Whenthe paint film has a single layered structure, the single layered paintfilm contains the polyurethane as the base resin. When the paint filmhas a multiple layered structure, at least the outermost paint filmlayer contains the polyurethane as the base resin.

The amount of the polyurethane in the base resin of the outermost paintfilm layer is preferably 50 mass % or more, more preferably 70 mass % ormore, and even more preferably 90 mass % or more. It is most preferablethat the base resin of the outermost paint film layer consists of thepolyurethane.

(Polyurethane)

The polyurethane contained in the outermost paint film layer will beexplained. The polyurethane is obtained by a reaction between (A) thepolyisocyanate composition and (B) the polyol composition. Theproperties of the paint film can be adjusted by changing the type orblended amount of the polyisocyanate component contained in (A) thepolyisocyanate composition or the polyol component contained in (B) thepolyol composition.

((A) Polyisocyanate Composition)

Examples of the polyisocyanate component of (A) the polyisocyanatecomposition include a compound having at least two isocyanate groups.Examples of the polyisocyanate include an aromatic polyisocyanate suchas 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (TDI),4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate(NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODD, xylylene diisocyanate(XDI), tetramethylxylylenediisocyanate (TMXDI), and para-phenylenediisocyanate (PPDI); an alicyclic polyisocyanate or aliphaticpolyisocyanate such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI),hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate(HDI), isophorone diisocyanate (IPDI), and norbornene diisocyanate(NBDI); and derivatives of these polyisocyanates. In the presentinvention, two or more polyisocyanates may be used as thepolyisocyanate.

Examples of the derivatives of the polyisocyanate include anadduct-modified product obtained by a reaction between a diisocyanateand a polyhydric alcohol; an isocyanurate-modified product of adiisocyanate; a biuret-modified product of a diisocyanate; and anallophanate-modified product of a diisocyanate. The derivatives of thepolyisocyanate from which free diisocyanate is removed are morepreferable.

The adduct-modified product is a polyisocyanate obtained by a reactionbetween a diisocyanate and a polyhydric alcohol. Preferable examples ofthe polyhydric alcohol include a low molecular weight triol such astrimethylolpropane and glycerin. As the adduct-modified product, anadduct-modified product of hexamethylene diisocyanate is preferable, atriisocyanate (the following formula (1)) obtained by a reaction betweenhexamethylene diisocyanate and trimethylolpropane; and a triisocyanate(the following formula (2)) obtained by a reaction between hexamethylenediisocyanate and glycerin are more preferable.

Examples of the isocyanurate-modified product include anisocyanurate-modified product of hexamethylene diisocyanate, and atrimer of hexamethylene diisocyanate (the following formula (3)) ispreferable.

Examples of the biuret-modified product include a trimerized product ofa diisocyanate, and a trimer of hexamethylene diisocyanate (thefollowing formula (4)) is preferable.

The allophanate-modified product is, for example, a triisocyanateobtained by further reacting a diisocyanate with a urethane bond formedby a reaction between a diisocyanate and a low molecular weight diol.

As the polyisocyanate component, the adduct-modified product ispreferable, and the adduct-modified product of hexamethylenediisocyanate (preferably trimer) is more preferable. When theadduct-modified product of hexamethylene diisocyanate is used, theamount of the adduct-modified product of hexamethylene diisocyanate inthe polyisocyanate component is preferably 30 mass % or more, morepreferably 40 mass % or more, and even more preferably 50 mass % ormore. It is also preferable that the polyisocyanate component consistsof the adduct-modified product of hexamethylene diisocyanate.

In addition, as the polyisocyanate component, the adduct-modifiedproduct and the isocyanurate-modified product are preferably used incombination, and the adduct-modified product of hexamethylenediisocyanate (the trimer is preferable) and the isocyanurate-modifiedproduct of hexamethylene diisocyanate (the trimer is preferable) aremore preferably used in combination. In this case, the mass ratio(adduct-modified product/isocyanurate-modified product) of theadduct-modified product to the isocyanurate-modified product ispreferably 0.43 or more, more preferably 1.0 or more, and even morepreferably 2.5 or more. If the mass ratio is 0.43 or more, the dynamicfriction coefficient is greater and thus the spin rate on approach shotsunder a condition that there is grass between the golf ball and the clubface increases.

In addition, when the adduct-modified product of hexamethylenediisocyanate and the isocyanurate-modified product of hexamethylenediisocyanate are used as the polyisocyanate component, the total amountof the adduct-modified product of hexamethylene diisocyanate and theisocyanurate-modified product of hexamethylene diisocyanate in thepolyisocyanate component is preferably 70 mass % or more, morepreferably 80 mass % or more, and even more preferably 90 mass % ormore. It is also preferable that the polyisocyanate component consistsof the adduct-modified product of hexamethylene diisocyanate and theisocyanurate-modified product of hexamethylene diisocyanate.

The amount (NCO %) of the isocyanate group of the polyisocyanatecomponent is preferably 0.5 mass % or more, more preferably 1.0 mass %or more, and even more preferably 2.0 mass % or more, and is preferably45 mass % or less, more preferably 40 mass % or less, and even morepreferably 35 mass % or less. It is noted that the amount (NCO %) of theisocyanate group of the polyisocyanate component can be represented by100×[mole number of isocyanate group in polyisocyanate×42 (molecularweight of NCO)]/[total mass (g) of polyisocyanate].

Specific examples of the polyisocyanate component include Burnock(Registered trademark) D-800, Burnock DN-950, and Burnock DN-955available from DIC corporation; Desmodur (Registered trademark)N75MPA/X, Desmodur N3300, Desmodur N3390, Desmodur L75 (C), and Sumidur(Registered trademark) E21-1 available from Sumika Bayer Urethane Co.,Ltd.; Coronate (Registered trademark) HX, Coronate HK, Coronate HL, andCoronate EH available from Tosoh Corporation; Duranate (Registeredtrademark) 24A-100, Duranate 21S-75E, Duranate TPA-100, DuranateTKA-100, Duranate 24A-90CX, and Duranate E402-80B available from AsahiKasei Chemicals Corporation; and VESTANAT (Registered trademark) T1890available from Degussa Co., Ltd.

((B) Polyol Composition)

The polyol composition contains a urethane polyol. If the urethanepolyol is used, the obtained paint film is soft and thus the spinperformance is enhanced. The urethane polyol is a compound having aplurality of urethane bonds in the molecule thereof, and having at leasttwo hydroxyl groups in one molecule.

Examples of the urethane polyol include a urethane prepolymer obtainedby a reaction between a first polyol component and a firstpolyisocyanate component, under a condition that the hydroxyl group ofthe first polyol component is excessive to the isocyanate group of thefirst polyisocyanate component.

The urethane polyol preferably has a polyether diol as a constituentcomponent. Examples of the polyether diol constituting the urethanepolyol include polyoxyethylene glycol, polyoxypropylene glycol, andpolyoxytetramethylene glycol. Among them, polyoxytetramethylene glycolis preferable.

The number average molecular weight of the polyether diol is preferably400 or more, more preferably 500 or more, and even more preferably 600or more, and is preferably 3000 or less, more preferably 2000 or less,even more preferably 1000 or less, and most preferably less than 800. Ifthe number average molecular weight of the polyether diol is 400 ormore, the impact durability of the paint film is enhanced, and if thenumber average molecular weight of the polyether diol is 3000 or less,the stain resistance of the paint film is enhanced. It is noted that theaverage molecular weight can be measured, for example, by gel permeationchromatography (GPC), using polystyrene as a standard material,tetrahydrofuran as an eluate, and an organic solvent system GPC column(e.g., “Shodex (registered trademark) KF series” available from ShowaDenko K.K.) as a column.

The urethane polyol may have a low molecular weight polyol having amolecular weight of less than 500 other than the polyether diol, as thefirst polyol component. Examples of the low molecular weight polyolinclude a diol such as ethylene glycol, diethylene glycol, triethyleneglycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, and1,6-hexanediol, and a triol such as glycerin, trimethylolpropane, andhexanetriol. The low molecular weight polyol may be used solely or as amixture of at least two of them.

The first polyol component constituting the urethane polyol preferablycontains a triol component and a diol component. As the triol component,trimethylolpropane is preferable. The mixing ratio (triol component/diolcomponent) of the triol component to the diol component is preferably0.2 or more, more preferably 0.5 or more, and is preferably 6.0 or less,more preferably 5.0 or less in a mass a ratio.

The first polyisocyanate component constituting the urethane polyol isnot particularly limited, as long as the first polyisocyanate componenthas at least two isocyanate groups. Examples of the first polyisocyanatecomponent include an aromatic polyisocyanate such as 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylenediisocyanate and 2,6-tolylene diisocyanate (TDI), 4,4′-diphenylmethanediisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI),3,3′-bitolylene-4,4′-diisocyanate (TODD, xylylene diisocyanate (XDI),tetramethylxylylenediisocyanate (TMXDI), and para-phenylene diisocyanate(PPDI); and an alicyclic polyisocyanate or aliphatic polyisocyanate suchas 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenatedxylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI),isophorone diisocyanate (IPDI), and norbornene diisocyanate (NED). Thesepolyisocyanates may be used solely or as a mixture of at least two ofthem.

The amount of the polyether diol in the urethane polyol is preferably 20mass % or more, more preferably 30 mass % or more, and even morepreferably 40 mass % or more. The polyether diol forms a soft segment inthe paint film. Therefore, if the amount of the polyether diol is 20mass % or more, the obtained golf ball has further enhanced spinperformance.

The weight average molecular weight of the urethane polyol is preferably5000 or more, more preferably 5300 or more, and even more preferably5500 or more, and is preferably 20000 or less, more preferably 18000 orless, and even more preferably 16000 or less. If the weight averagemolecular weight of the urethane polyol falls within the above range,the obtained golf ball has further enhanced spin performance.

The hydroxyl value of the urethane polyol is preferably 10 mgKOH/g ormore, more preferably 15 mgKOH/g or more, and even more preferably 20mgKOH/g or more, and is preferably 200 mgKOH/g or less, more preferably190 mgKOH/g or less, and even more preferably 180 mgKOH/g or less.

The polyol composition may contain a polyol compound other than theurethane polyol as the polyol component. Examples of the polyol compoundinclude a low molecular weight polyol having a molecular weight of lessthan 500 and a high molecular weight polyol having an average molecularweight of 500 or more. Examples of the low molecular weight polyolinclude a diol such as ethylene glycol, diethylene glycol, triethyleneglycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, and1,6-hexanediol, and a triol such as glycerin, trimethylolpropane, andhexanetriol. Examples of the high molecular weight polyol include apolyether polyol such as polyoxyethylene glycol (PEG), polyoxypropyleneglycol (PPG), and polyoxytetramethylene glycol (PTMG); a condensedpolyester polyol such as polyethylene adipate (PEA), polybutyleneadipate (PBA), and polyhexamethylene adipate (FNMA); a lactone polyesterpolyol such as poly-ε-caprolactone (PCL), a polycarbonate polyol such aspolyhexamethylene carbonate; and an acrylic polyol. The other polyolcompound may be used solely or as a mixture of at least two of them.

The amount of the urethane polyol in the polyol component contained inthe polyol composition is preferably 60 mass % or more, more preferably70 mass % or more, and even more preferably 80 mass % or more. It isalso preferable that the polyol component of the polyol compositionconsists of the urethane polyol.

The hydroxyl value of the polyol component contained in the polyolcomposition is preferably 10 mgKOH/g or more, more preferably 15 mgKOH/gor more, and even more preferably 20 mgKOH/g or more, and is preferably400 mgKOH/g or less, preferably 300 mgKOH/g or less, more preferably 200mgKOH/g or less, even more preferably 170 mgKOH/g or less, and mostpreferably 160 mgKOH/g or less. If the hydroxyl value of the polyolcomponent falls within the above range, the paint film has enhancedadhesion to the golf ball body. It is noted that in the presentinvention, the hydroxyl value can be measured according to JIS K 1557-1,for example, by an acetylation method.

The molar ratio (NCO group/OH group) of the isocyanate group (NCO group)included in (A) the polyisocyanate composition to the hydroxyl group (OHgroup) included in (B) the polyol composition is preferably 0.1 or more,more preferably 0.5 or more, and even more preferably 1.1 or more. Ifthe molar ratio (NCO group/OH group) is 0.1 or more, the curing reactionsufficiently proceeds. In addition, if the molar ratio (NCO group/OHgroup) is excessively large, the amount of the isocyanate group isexcessive, and the obtained paint film not only becomes hard and fragilebut also has deteriorated poor appearance. Thus, the molar ratio (NCOgroup/OH group) is preferably 2.0 or less, more preferably 1.7 or less,and even more preferably 1.5 or less. It is noted that the reason whythe appearance of the obtained paint film deteriorates if the amount ofthe isocyanate group in the paint becomes excessive is that an excessiveamount of the isocyanate group may promote a reaction between themoisture in air and the isocyanate group, thereby generating a lot ofcarbon dioxide gas.

(A) The polyisocyanate composition and (B) the polyol composition maycontain a solvent. The solvent may be water or an organic solvent, andis preferably the organic solvent. Examples of the organic solventinclude toluene, isopropyl alcohol, xylene, methylethyl ketone,methylethylisobutyl ketone, ethylene glycol monomethyl ether,ethylbenzene, propylene glycol monomethyl ether, isobutyl alcohol, andethyl acetate. It is noted that the solvent may be added in either of(A) the polyisocyanate composition and (B) the polyol composition, andin light of uniformly performing the curing reaction, the solvent ispreferably added in the polyol composition and the polyisocyanatecomposition, respectively.

(A) The polyisocyanate composition and (B) the polyol composition maycontain a catalyst for the curing reaction. Examples of the catalystinclude a monoamine such as triethyl amine andN,N-dimethylcyclohexylamine; a polyamine such asN,N,N′,N′-tetramethylethylene diamine and N,N,N′,N″,N″-pentamethyldiethylene triamine; a cyclic diamine such as1,8-diazabicyclo[5.4.0]-7-undecene (DBU) and triethylene diamine; and atin catalyst such as dibutyl tin dilaurate and dibutyl tin diacetate.These catalysts may be used solely, or two or more of the catalysts maybe used in combination. Among them, the tin catalyst such as dibutyl tindilaurate and dibutyl tin diacetate is preferable, and dibutyl tindilaurate is particularly preferable.

(A) The polyisocyanate composition and (B) the polyol composition mayfurther contain additives generally contained in a paint for a golfball, such as a filler, an ultraviolet absorber, an antioxidant, a lightstabilizer, a fluorescent brightener, an anti-blocking agent, a levelingagent, a slip agent, and a viscosity modifier, where necessary.

The outermost paint film layer is preferably formed from a paintcontaining (A) the polyisocyanate composition and (B) the polyolcomposition. Examples of the paint include a so-called two-componentcuring type urethane paint containing the polyol as a base material andthe polyisocyanate as a curing agent.

(Properties of the Outermost Paint Film Layer)

The dynamic friction coefficient of the outermost paint film layer ispreferably 0.65 or more, more preferably 0.70 or more, and even morepreferably 0.73 or more, and is preferably 1.2 or less, more preferably1.1 or less, and even more preferably 1.0 or less. If the dynamicfriction coefficient is less than 0.65, the spin rate on approach shotsunder a condition that there is grass between the golf ball and the clubface decreases, and if the dynamic friction coefficient is more than1.2, the paint film has strong adhesiveness and thus is easily stained.

The peak temperature of the loss tangent (tan δ) of the outermost paintfilm layer is preferably −40° C. or more, more preferably −30° C. ormore, and even more preferably −20° C. or more, and is preferably 40° C.or less, more preferably 30° C. or less, and even more preferably 20° C.or less. If the peak temperature of the loss tangent (tan δ) is −40° C.or more, the paint film has low adhesiveness and thus is hard to bestained, and if the peak temperature of the loss tangent (tan δ) is 40°C. or less, the paint film has a high dynamic friction coefficient andthus the spin rate on approach shots under a condition that there isgrass between the golf ball and the club face increases.

The storage modulus (E′) of the outermost paint film layer at thetemperature of 24° C. is preferably 10 MPa or more, more preferably 15MPa or more, and even more preferably 20 MPa or more, and is preferably100 MPa or less, more preferably 80 MPa or less, and even morepreferably 60 MPa or less. If the storage modulus (E′) is 10 MPa ormore, the paint film has low adhesiveness and thus is hard to bestained, and if the storage modulus (E′) is 100 MPa or less, the paintfilm has a high dynamic friction coefficient and thus the spin rate onapproach shots under a condition that there is grass between the golfball and the club face increases.

The loss modulus (E″) of the outermost paint film layer at thetemperature of 24° C. is preferably 0.1 MPa or more, more preferably 0.5MPa or more, and even more preferably 1.0 MPa or more, and is preferably80 MPa or less, more preferably 65 MPa or less, and even more preferably50 MPa or less. If the loss modulus (E″) is 0.1 MPa or more, the paintfilm has low adhesiveness and thus is hard to be stained, and if theloss modulus (E″) is 80 MPa or less, the paint film has a high dynamicfriction coefficient and thus the spin rate on approach shots under acondition that there is grass between the golf ball and the club faceincreases.

The 10% elastic modulus of the outermost paint film layer is preferably1 kgf/cm² (0.10 MPa) or more, more preferably 3 kgf/cm² (0.29 MPa) ormore, and even more preferably 5 kgf/cm² (0.49 MPa) or more, and ispreferably 50 kgf/cm² (4.9 MPa) or less, more preferably 40 kgf/cm² (3.9MPa) or less, and even more preferably 30 kgf/cm² (2.9 MPa) or less. Ifthe 10% elastic modulus of the outermost paint film layer is 1 kgf/cm²or more, the paint film has low adhesiveness and thus is hard to bestained, and if the 10% elastic modulus of the outermost paint filmlayer is 50 kgf/cm² or less, the paint film has a high dynamic frictioncoefficient and thus the spin rate on approach shots under a conditionthat there is grass between the golf ball and the club face increases.

The thickness of the outermost paint film layer is preferably 5 μm ormore, more preferably 7 μm or more, and is preferably 40 μm or less,more preferably 30 μm or less, and even more preferably 20 μm or less.If the thickness of the outermost paint film layer falls within theabove range, the outermost paint film layer has better appearance, andthe golf ball has better abrasion resistance and better approachperformance.

The methods for measuring the dynamic friction coefficient, losstangent, storage modulus, loss modulus and thickness of the outermostpaint film layer will be described later.

When the paint film has a multiple layered structure, examples of thebase resin constituting the paint film layer other than the outermostpaint film layer include a urethane resin, an epoxy resin, an acrylicresin, a vinyl acetate resin, and a polyester resin, and among them, theurethane resin is preferable. The paint film layer other than theoutermost paint film layer may be formed from a paint same as ordifferent from the paint for forming the outermost paint film layer.

(Formation of Paint Film)

The paint film can be formed by applying a paint on the surface of thegolf ball body. The method of applying the paint is not particularlylimited, a conventional method can be adopted, and examples thereofinclude a spray coating and electrostatic coating.

In the case of performing the spray coating with an air gun, (A) thepolyisocyanate composition and (B) the polyol composition are fed withrespective pumps and continuously mixed with a line mixer located in thestream line just before the air gun, and the obtained mixture isair-sprayed. Alternatively, the polyol and the polyisocyanate areair-sprayed respectively with an air spray system provided with a devicefor controlling the mixing ratio thereof. The paint application may beconducted by spraying the paint one time or overspraying the paintmultiple times.

The paint applied on the golf ball body can be dried, for example, at atemperature in a range of from 30° C. to 70° C. for 1 hour to 24 hours,to form the paint film.

(Golf Ball Body)

The golf ball according to the present invention is not particularlylimited, as long as it is a golf ball comprising a golf ball body and apaint film formed on a surface of the golf ball body. The constructionof the golf ball body is not particularly limited, and the golf ballbody may be a one-piece golf ball, a two-piece golf ball, a multi-piecegolf ball such as a three-piece golf ball, a four-piece golf ball, afive-piece golf ball and a golf ball comprising more than five pieces,or a wound golf ball. The present invention can be applied appropriatelyto any one of the above golf balls.

(Core)

The one-piece golf ball body and the core used for a wound golf ball,two-piece golf ball and multi-piece golf ball will be explained.

The one-piece golf ball body or the core may be formed from aconventionally known rubber composition (hereinafter sometimes simplyreferred to as “core rubber composition”). For example, the one-piecegolf ball body or the core may be formed by heat pressing a rubbercomposition containing a base rubber, a co-crosslinking agent and acrosslinking initiator.

As the base rubber, particularly preferable is a high cis-polybutadienehaving a cis-bond in a proportion of 40 mass % or more, more preferably70 mass % or more, and even more preferably 90 mass % or more in view ofits advantageous resilience. As the co-crosslinking agent, anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metalsalt thereof is preferable, and a metal salt of acrylic acid or a metalsalt of methacrylic acid is more preferable. As the metal constitutingthe metal salt, zinc, magnesium, calcium, aluminum or sodium ispreferable, and zinc is more preferable. The amount of theco-crosslinking agent is preferably 20 parts by mass or more and 50parts by mass or less with respect to 100 parts by mass of the baserubber. In the case that the α,β-unsaturated carboxylic acid having 3 to8 carbon atoms is used as the co-crosslinking agent, a metal compound(e.g. magnesium oxide) is preferably used in combination. As thecrosslinking initiator, an organic peroxide is preferably used. Specificexamples of the organic peroxide include dicumyl peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Amongthem, dicumyl peroxide is preferably used. The amount of thecrosslinking initiator is preferably 0.2 part by mass or more, morepreferably 0.3 part by mass or more, and is preferably 3 parts by massor less, more preferably 2 parts by mass or less, with respect to 100parts by mass of the base rubber.

In addition, the core rubber composition may further contain an organicsulfur compound. As the organic sulfur compound, diphenyl disulfides(e.g. diphenyl disulfide, bis(pentabromophenyl)disulfide), thiophenolsor thionaphthols (e.g. 2-thionaphthol) are preferably used. The amountof the organic sulfur compound is preferably 0.1 part by mass or more,more preferably 0.3 part by mass or more, and is preferably 5.0 parts bymass or less, more preferably 3.0 parts by mass or less, with respect to100 parts by mass of the base rubber. The core rubber composition mayfurther contain a carboxylic acid and/or a salt thereof. As thecarboxylic acid and/or the salt thereof, a carboxylic acid having 1 to30 carbon atoms and/or a salt thereof is preferable. As the carboxylicacid, an aliphatic carboxylic acid or an aromatic carboxylic acid (e.g.benzoic acid) may be used. The amount of the carboxylic acid and/or thesalt thereof is preferably 1 part by mass or more and 40 parts by massor less with respect to 100 parts by mass of the base rubber.

The core rubber composition may further contain a weight adjusting agentsuch as zinc oxide and barium sulfate, an antioxidant, or a coloredpowder, in addition to the base rubber, the co-crosslinking agent, thecrosslinking initiator, and the organic sulfur compound. The moldingconditions for heat pressing the core rubber composition may beappropriately set depending on the rubber formulation. Generally, theheat pressing is preferably carried out at 130° C. to 200° C. for 10 to60 minutes, or carried out in a two-step heating of heating at 130° C.to 150° C. for 20 to 40 minutes followed by heating at 160° C. to 180°C. for 5 to 15 minutes.

(Cover)

The golf ball body preferably comprises a core and a cover covering thecore. In this case, the hardness of the cover is preferably 60 or less,more preferably 55 or less, even more preferably 50 or less, and mostpreferably 45 or less in Shore D hardness. If the hardness of the coveris 60 or less in Shore D hardness, the spin rate is further increased.The lower limit of the hardness of the cover is not particularlylimited, and is preferably 10, more preferably 15, and even morepreferably 20 in Shore D hardness. The hardness of the cover is a slabhardness of the cover composition molded into a sheet shape.

The thickness of the cover is preferably 0.1 mm or more, more preferably0.2 mm or more, and even more preferably 0.3 mm or more, and ispreferably 1.0 mm or less, more preferably 0.9 mm or less, and even morepreferably 0.8 mm or less. If the thickness of the cover is 0.1 mm ormore, the shot feeling of the golf ball is better, and if the thicknessof the cover is 1.0 mm or less, the resilience of the golf ball ismaintained.

The resin component constituting the cover is not particularly limited,and examples thereof include various resins such as an ionomer resin, apolyester resin, a urethane resin and a polyamide resin; a thermoplasticpolyamide elastomer having a trade name of “Pebax (registered trademark)(e.g. “Pebax 2533”)” available from Arkema Inc.; a thermoplasticpolyester elastomer having a trade name of “Hytrel (registeredtrademark) (e.g. “Hytrel 3548” and “Hytrel 4047”)” available from DuPont-Toray Co., Ltd.; a thermoplastic polyurethane elastomer having atrade name of “Elastollan (registered trademark) (e.g. “ElastollanXNY97A”)” available from BASF Japan Ltd.; and a thermoplastic styreneelastomer having a trade name of “Rabalon (registered trademark)” and athermoplastic polyester elastomer having a trade name of “Primalloy”both available from Mitsubishi Chemical Corporation. These covermaterials may be used solely, or two or more of these cover materialsmay be used in combination.

Among them, the resin component constituting the cover is preferably thepolyurethane resin or the ionomer resin, particularly preferably thepolyurethane resin. When the resin component constituting the coverincludes the polyurethane resin, the amount of the polyurethane resin inthe resin component is preferably 50 mass % or more, more preferably 70mass % or more, and even more preferably 90 mass % or more. When theresin component constituting the cover includes the ionomer resin, theamount of the ionomer resin in the resin component is preferably 50 mass% or more, more preferably 70 mass % or more, and even more preferably90 mass % or more.

The polyurethane may be either a thermoplastic polyurethane or athermosetting polyurethane. The thermoplastic polyurethane is apolyurethane exhibiting plasticity by heating and generally means apolyurethane having a linear chain structure of a high-molecular weightto a certain extent. On the other hand, the thermosetting polyurethane(two-component curing type polyurethane) is a polyurethane obtained bypolymerization through a reaction between a low-molecular weighturethane prepolymer and a curing agent (chain extender) when molding thecover. The thermosetting polyurethane includes a polyurethane having alinear chain structure or a polyurethane having a three-dimensionalcrosslinked structure depending on the number of the functional group ofthe prepolymer or the curing agent (chain extender) to be used. As thepolyurethane, the thermoplastic elastomer is preferable.

The cover may further contain a pigment component such as a whitepigment (e.g. titanium oxide), a blue pigment and a red pigment, aweight adjusting agent such as calcium carbonate and barium sulfate, adispersant, an antioxidant, an ultraviolet absorber, a light stabilizer,a fluorescent material or a fluorescent brightener, or the like, inaddition to the above resin component, as long as they do not impair theperformance of the cover.

The method for molding the cover from the cover composition is notparticularly limited, and examples thereof include a method of injectionmolding the cover composition directly onto the core; and a method ofmolding the cover composition into hollow shells, covering the core witha plurality of the hollow shells and compression molding the core with aplurality of the hollow shells (preferably a method of molding the covercomposition into half hollow-shells, covering the core with two of thehalf hollow-shells and compression molding the core with two of the halfhollow-shells). The golf ball body having the cover formed thereon isejected from the mold, and as necessary, the golf ball body ispreferably subjected to surface treatments such as deburring, cleaning,and sandblast. In addition, if desired, a mark may also be formedthereon.

The total number of the dimples formed on the cover is preferably 200 ormore and 500 or less. If the total number of the dimples is less than200, the dimple effect is hardly obtained, and if the total number ofthe dimples exceeds 500, the dimple effect is hardly obtained becausethe size of the respective dimples is small. The shape (shape in a planview) of the dimples includes, for example, but is not limited to, acircle; a polygonal shape such as a roughly triangular shape, a roughlyquadrangular shape, a roughly pentagonal shape, and a roughly hexagonalshape; and other irregular shape. The shape of the dimples may beemployed solely, or two or more of the shapes may be employed incombination.

When the golf ball is a multi-piece golf ball such as a three-piece golfball, a four-piece golf ball, a five-piece golf ball and a golf ballcomposed of more than five pieces, examples of the material for formingthe intermediate layer disposed between the core and the outermost coverinclude a thermoplastic resin such as a polyurethane resin, an ionomerresin, a polyamide resin, and a polyethylene; a thermoplastic elastomersuch as a styrene elastomer, a polyolefin elastomer, a polyurethaneelastomer, and a polyester elastomer; and a cured product of a rubbercomposition. Herein, examples of the ionomer resin include a productobtained by neutralizing at least a part of carboxyl groups of acopolymer composed of ethylene and an α,β-unsaturated carboxylic acidwith a metal ion; and a product obtained by neutralizing at least a partof carboxyl groups of a ternary copolymer composed of ethylene, anα,β-unsaturated carboxylic acid and an α,β-unsaturated carboxylic acidester with a metal ion. The intermediate layer may further contain aweight adjusting agent such as barium sulfate and tungsten, anantioxidant, a pigment, and the like. It is noted that the intermediatelayer is sometimes referred to as an inner cover layer or an outer corelayer, depending on the construction of the golf ball.

The golf ball preferably has a diameter in a range from 40 mm to 45 mm.In light of satisfying the regulation of US Golf Association (USGA), thediameter is particularly preferably 42.67 mm or more. In light ofprevention of air resistance, the diameter is more preferably 44 mm orless, even more preferably 42.80 mm or less. In addition, the golf ballaccording to the present invention preferably has a mass of 40 g or moreand 50 g or less. In light of obtaining greater inertia, the mass ismore preferably 44 g or more, even more preferably 45.00 g or more. Inlight of satisfying the regulation of USGA, the mass is particularlypreferably 45.93 g or less.

When the golf ball has a diameter in a range from 40 mm to 45 mm, thecompression deformation amount (shrinking amount along the compressiondirection) of the golf ball when applying a load from 98 N as an initialload to 1275 N as a final load to the golf ball is preferably 2.0 mm ormore, more preferably 2.2 mm or more, and is preferably 4.0 mm or less,more preferably 3.5 mm or less. If the compression deformation amount is2.0 mm or more, the golf ball is not excessively hard and thus the shotfeeling thereof is better. On the other hand, if the compressiondeformation amount is 4.0 mm or less, the resilience is greater.

The FIGURE is a partially cutaway cross-sectional view showing a golfball 1 according to one embodiment of the present invention. The golfball 1 comprises a spherical core 2, a cover 3 covering the sphericalcore 2, and a paint film 4 formed on a surface of the cover 3. On thesurface of the cover 3, a plurality of dimples 31 are formed. On thesurface of the cover 3, a part other than the dimples 31 is a land 32.

EXAMPLES

Next, the present invention will be described in detail by way ofexamples. However, the present invention is not limited to the examplesdescribed below. Various changes and modifications without departingfrom the spirit of the present invention are included in the scope ofthe present invention.

[Evaluation Method]

(1) Compression Deformation Amount (Mm)

The deformation amount of the core along the compression direction(shrinking amount of the core along the compression direction), whenapplying a load from 98 N as an initial load to 1275 N as a final loadto the core, was measured.

(2) Core Hardness (Shore C Hardness)

The hardness measured at the surface of the core was adopted as thesurface hardness of the core. In addition, the core was cut into twohemispheres and the hardness measured at the central point of theobtained cut plane was adopted as the center hardness of the core. Thehardness was measured with an automatic hardness tester (Digitest IIavailable from Bareiss company) using a detector of “Shore C”.

(3) Slab Hardness (Shore D Hardness)

Sheets with a thickness of about 2 mm were produced by injection moldingthe resin composition. The sheets were stored at 23° C. for two weeks.At least three of these sheets were stacked on one another so as not tobe affected by the measuring substrate on which the sheets were placed,and the hardness of the stack was measured with an automatic hardnesstester (Digitest II available from Bareiss company) using a detector of“Shore D”.

(4) Thickness of Paint Film (μm)

The golf ball was cut into two hemispheres, and the cross section of thepaint film on the hemisphere was observed with a microscope (VHX-1000available from Keyence Corporation) to obtain the thickness of the paintfilm.

(5) Loss Tangent (Tan δ)

The storage modulus E′ (Pa), loss modulus E″ (Pa) and loss tangent (tanδ) of the paint film were measured under the following conditions.

Apparatus: Dynamic viscoelasticity measuring apparatus (Rheogel-E4000available from UBM CO., Ltd.)

Test sample: A paint obtained by blending the polyisocyanate compositionand the polyol composition was dried and cured at the temperature of 40°C. for 4 hours to prepare a paint film having a thickness ranging from0.11 mm to 0.14 mm. The paint film was cut to prepare a test piecehaving a width of 4 mm and a distance between the clamps of 20 mm.

Measuring mode: tensile mode

Measuring temperature: −100° C. to 150° C.

Temperature increase rate: 4° C./min

Measuring date capturing interval: 4° C.

Oscillation frequency: 10 Hz

Measuring strain: 0.1%

(6) 10% Elastic Modulus of Paint Film

The tensile properties of the paint film were measured according to JISK7161 (2014). Specifically, the polyisocyanate composition and thepolyol composition were blended to prepare a paint, and the obtainedpaint was dried and cured at the temperature of 40° C. for 4 hours toprepare a paint film (thickness: 0.05 mm). The paint film was punchedinto the test piece type II (width of parallel part: 10 mm, gaugelength: 50 mm) prescribed in JIS K7127 (1999), to prepare a test piece.The tensile test of the test piece was conducted with a precisionuniversal tester (Autograph (registered trademark) available fromShimadzu Corporation) under testing conditions of a length betweengrips: 100 mm, a tensile speed: 50 mm/min and a testing temperature: 23°C., and the tensile stress at 10% strain (10% elastic modulus) wasrecorded.

(7) Spin Rate Under Dry Condition

A sand wedge (trade name: “CG 15 forged wedge”, loft angel: 52°available from Cleveland Golf Inc.) was installed on a swing machineavailable from Golf Laboratories, Inc. The golf ball was hit at a headspeed of 16 m/s, and the spin rate (rpm) thereof was measured bycontinuously taking a sequence of photographs of the hit golf ball. Themeasurement was conducted ten times for each golf ball, and the averagevalue thereof was adopted as the spin rate.

(8) Spin Rate Under a Condition that there is Grass Between the GolfBall and the Club Face

A sand wedge (trade name: “CG 15 forged wedge”, loft angel: 52°available from Cleveland Golf Inc.) was installed on a swing machineavailable from Golf Laboratories, Inc. The golf ball was hit at a headspeed of 16 m/s, and the spin rate (rpm) thereof was measured bycontinuously taking a sequence of photographs of the hit golf ball. Itis noted that two leaves (length: about 3 cm) of wild grass wereattached to the golf ball that was the testing object, and the golf ballwas hit such that there was the wild grass between the club face and thegolf ball. The measurement was conducted ten times for each golf ball,and the average value thereof was adopted as the spin rate.

(9) Dynamic Friction Coefficient

The dynamic friction coefficient of the golf ball was measured under thefollowing conditions. It is noted that in the following conditions, theload is small and the moving speed is low, thus the dynamic frictioncoefficient of the outermost paint film layer can be measured.

-   -   Tester: Tribo Master TL201TS (available from Trinity-Lab inc.)    -   Test sample: golf ball    -   Face plate: A plate made of stainless steel (HT1770 (size: 50        mm×150 mm×thickness 2 mm) available from Nippon Steel Nisshin        Co., Ltd.) and having a face surface with an arithmetic mean        roughness Ra of 2.9 μm and a maximum height mean value Ry of        21.7 μm was used.    -   Preparation method of face plate: The face plate was obtained by        performing an air-blast treatment to the stainless steel. As the        grinding material, a mixture of alumina powder (#60) and steel        ball (ES300 available from Ervin industries Co., Ltd.) in a        mixing ratio of 1:1 was used. The blasting conditions were: a        distance of 10 cm between the face plate and the nozzle, and a        pressure of 4 to 6 kg/cm² just before the nozzle.    -   Measuring method of Ra and Ry: Ra and Ry were measured with a        surface roughness tester (SJ-301 available from Mitutoyo        Corporation) by a method based on JIS B 0601-1994. Ra, Ry were        each an average value of the values obtained at six measuring        points. In addition, the cutoff vale λc was 2.5 mm.    -   Temperature: 23° C.    -   Ball moving speed: 2 mm/s    -   Load: 1.96 N (200 gf)    -   Measurement method: The ball was fixed with a chuck, and allowed        to move at a predetermined speed on a flat plate in a state that        200 gf of a load was applied on the ball, to measure the dynamic        friction force.    -   Measuring item: dynamic friction (average value in the section        of from 2-10 mm)        [Production of Golf Ball]        1. Production of Spherical Core

The rubber composition having the formulation shown in Table 1 waskneaded, and heat-pressed at the temperature of 150° C. for 19 min inupper and lower molds, each having a hemispherical cavity, to obtain aspherical core having a diameter of 39.7 mm. It is noted that the amountof barium sulfate was adjusted such that the ball had a mass of 45.6 g.

TABLE 1 Spherical core Rubber Polybutadiene rubber 100 composition Zincacrylate 30.5 formulation (parts Zinc oxide 10 by mass) Barium sulfateAppropriate amount Bis(pentabromophenyl) 0.3 disulfide Dicumyl peroxide0.7 Benzoic acid 2 Molding Temperature (° C.) 150 condition Time (min)19 Core properties Compression deformation 3.3 amount (mm) Centerhardness (Shore C) 53 Surface hardness (Shore C) 80 Hardness difference(Surface - 27 center) (Shore C)

Polybutadiene rubber: “BR730 (high-cis polybutadiene)” available fromJSR Corporation

Zinc acrylate: “ZN-DA90S” available from Nihon Jyoryu Kogyo Co., Ltd.

Zinc oxide: “Ginrei R” available from Toho Zinc Co., Ltd.

Barium sulfate: “Barium Sulfate BD” available from Sakai ChemicalIndustry Co., Ltd.

Bis(pentabromophenyl)disulfide: available from Kawaguchi ChemicalIndustry Co., Ltd.

Dicumyl peroxide: “Percumyl (register trademark) D” available from NOFCorporation

Benzoic acid: available from Emerald Kalama Chemical Co., Ltd.

2. Preparation of Intermediate Layer Composition and Cover Composition

According to the formulations shown in Tables 2 and 3, the materialswere mixed with a twin-screw kneading extruder to prepare theintermediate layer composition and the cover composition in a pelletform. The extruding conditions were a screw diameter of 45 mm, a screwrotational speed of 200 rpm, and a screw L/D=35, and the mixture washeated to 160° C. to 230° C. at the die position of the extruder.

TABLE 2 Intermediate layer composition (parts by mass) Himilan AM7329 55Himilan 1555 45 Barium sulfate Appropriate amount Titanium dioxide 3Slab hardness (Shore D) 62

Himilan (registered trademark) AM7329: zinc ion-neutralizedethylene-methacrylic acid copolymer ionomer resin available from DuPont-Mitsui Polychemicals Co., Ltd.

Himilan 1555: sodium ion-neutralized ethylene-methacrylic acid copolymerionomer resin available from Du Pont-Mitsui Polychemicals Co., Ltd.

TABLE 3 Cover composition (parts by mass) Elastollan NY80A 100 Titaniumdioxide 4 Ultramarine blue 0.04 Slab hardness (Shore D) 27

Elastollan (registered trademark) NY80A: thermoplastic polyurethaneelastomer available from BASF Japan Ltd.

3. Molding of Intermediate Layer

The intermediate layer composition obtained above was directly injectionmolded onto the spherical core obtained above to form the intermediatelayer (thickness: 1.0 mm) covering the spherical core.

4. Production of Reinforcing Layer

A reinforcing layer composition (trade name “Polin (registeredtrademark) 750LE” available from Shinto Paint Co., Ltd.) having atwo-component curing type epoxy resin as the base resin was prepared.The base agent contains a bisphenol A type solid epoxy resin in anamount of 30 parts by mass, and a solvent in an amount of 70 parts bymass. The curing agent contains a modified polyamide amine in an amountof 40 parts by mass, titanium dioxide in an amount of 5 parts by mass,and a solvent in an amount of 55 parts by mass. The mass ratio of thebase agent to the curing agent was 1/1. The reinforcing layercomposition was applied to the surface of the intermediate layer with anair gun, and kept for 12 hours in an atmosphere of 23° C., to form thereinforcing layer. The thickness of the reinforcing layer was 7 μm.

5. Molding of Cover

The cover composition in the pellet form was charged into each of thedepressed part of the lower mold for molding half shells, and a pressurewas applied to mold half shells. The spherical body having thereinforcing layer formed thereon was concentrically covered with two ofthe half shells. The spherical body and the half shells were chargedinto a final mold provided with a plurality of pimples on the cavitysurface. The cover (thickness: 0.5 mm) was formed by compression moldingto obtain golf ball bodies. A plurality of dimples having an invertedshape of the pimples were formed on the cover.

6. Preparation of Urethane Polyol

As the first polyol component, polytetramethylene ether glycol (PTMG)and trimethylolpropane (TMP) were dissolved in a solvent (toluene andmethyl ethyl ketone). In the obtained solution, as a catalyst,dibutyltin dilaurate was added in an amount of 0.1 mass % with respectto the total amount of the base material. While keeping the temperatureof the obtained polyol solution at the temperature of 80° C., isophoronediisocyanate (IPDI), as the first polyisocyanate component, was addeddropwise to the polyol solution and mixed. After finishing the additionof isophorone diisocyanate, stirring was continued until the isocyanategroup no longer existed. Then, the reaction liquid was cooled to theroom temperature to prepare the urethane polyol (solid content: 30 mass%). The composition and the characteristics of the obtained urethanepolyol are shown in Table 4.

TABLE 4 Urethane polyol Component Polyol component PTMG TMPPolyisocyanate component IPDI Number average molecular weight of PTMG650 TMP: PTMG (molar ratio) 1.87:1 Molar ratio (NCO/OH) of NCO group in0.6 polyisocyanate component to OH group in polyol component Amount ofPTMG (mass %) 46.2 Hydroxyl value of solid component (mgKOH/g) 128.0Weight average molecular weight 72007. Formation of Paint Film

Materials shown in Table 5 were blended to prepare paint compositionsNo. 1 to No. 8. The surface of the golf ball bodies obtained above wastreated with sandblast and marked. The paint was applied with a spraygun, and dried for 24 hours in an oven at the temperature of 40° C. toobtain golf balls having a diameter of 42.7 mm and a mass of 45.6 g.

The application of the paint was conducted as follows. The golf ballbody was placed in a rotating member provided with a prong, and therotating member was allowed to rotate at 300 rpm. The application of thepaint was conducted by spacing a spray distance (7 cm) between the airgun and the golf ball body, and moving the air gun in an up and downdirection. The painting interval in the overpainting operation was setto 1.0 second. The application of the paint was conducted under thespraying conditions of overpainting operation: twice, spraying airpressure: 0.15 MPa, compressed air tank pressure: 0.10 MPa, paintingtime per one application: one second, atmosphere temperature: 20° C. to27° C., and atmosphere humidity: 65% or less. Evaluation resultsregarding the spin performance of the obtained golf balls are shown inTable 5.

TABLE 5 Golf ball No. 1 2 3 4 5 6 7 8 Paint Polyol Urethane polyol 100100 100 100 70 100 100 100 composition Liquid polybutadiene — — — — 30 —— — (parts by mass) Polyisocyanate Adduct-modified product of HDI 100 7030 — — — — — composition Biuret-modified product of HDI — — — — 30 30 3030 (parts by mass) Isocyanurate-modified product of — 30 70 100 30 30 3030 HDI Isocyanurate-modified product of — — — — 40 40 40 40 IPDIPolyisocyanate composition/polyol composition 1.2/1.0 1.2/1.0 1.2/1.01.2/1.0 0.7/1.0 0.38/1.0 0.61/1.0 1.2/1.0 blending ratio (NCO/OH molarratio) Paint film Thickness (μm) 10 10 10 10 10 10 10 10 properties Peaktemperature of loss tangent (tanδ) (° C.) 8 14 20 32 64 52 68 84 Storagemodulus E′ at 24° C. (MPa) 23 28 34 45 325 198 595 1520 Loss modulus E″at 24° C. (MPa) 10 14 18 21 93 88 95 114 10% Elastic modulus (kgf/cm²) 710 12 15 55 10 65 180 Dynamic friction coefficient of the outermostpaint film 1.02 0.93 0.83 0.73 0.62 0.62 0.57 0.62 layer Golf ball Spinrate under a dry condition (rpm) 4600 4650 4700 4700 4680 4650 4680 4600evaluation Spin rate under a condition that there is grass between 37003600 3500 3300 2800 3000 2800 2600 the golf ball and the club face (rpm)Spin rate retention ratio under a condition that there is 80.4 77.4 74.570.2 59.8 64.5 59.8 56.5 grass between the golf ball and the club face(%)

The materials used in Table 5 are shown as below.

Polyol Composition

Liquid polybutadiene: Poly bd (registered trademark) R-45HT (hydroxylgroup terminated liquid polybutadiene) available from Idemitsu KosanCo., Ltd.

Polyisocyanate Composition

Adduct-modified product of HDI: adduct-modified product of hexamethylenediisocyanate (Duranate (registered trademark) E402-80B (NCO amount:7.3%) available from Asahi Kasei Chemicals Corporation)

Biuret-modified product of HDI: biuret-modified product of hexamethylenediisocyanate (Duranate (registered trademark) 21S-75E (NCO amount:15.5%) available from Asahi Kasei Chemicals Corporation)

Isocyanurate-modified product of HDI: isocyanurate-modified product ofhexamethylene diisocyanate (Duranate TKA-100 (NCO amount: 21.7%)available from Asahi Kasei Chemicals Corporation)

Isocyanurate-modified product of IPDI: isocyanurate-modified product ofisophorone diisocyanate (VESTANAT (registered trademark) T1890 (NCOamount: 12.0%) available from Degussa Co., Ltd.)

Solvent: methylethyl ketone

The golf balls No. 1 to 4 are the cases that the base resin of theoutermost paint film layer contains a polyurethane having a urethanepolyol as a polyol component, and the dynamic friction coefficient ofthe outermost paint film layer is controlled to from 0.65 to 1.2. Thesegolf balls No. 1 to 4 are excellent in both the approach spinperformance under a dry condition and the approach spin performanceunder a condition that there is grass between the golf ball and the clubface.

The golf balls No. 5 to 8 are the cases that the dynamic frictioncoefficient of the outermost paint film layer is less than 0.65. Thesegolf balls No. 5 to 8 are excellent in the approach spin performanceunder a dry condition, but is poor in the approach spin performanceunder a condition that there is grass between the golf ball and the clubface.

This application is based on Japanese patent application No. 2018-207334filed on Nov. 2, 2018, the contents of which are hereby incorporated byreference.

The invention claimed is:
 1. A golf ball comprising a golf ball body anda paint film formed on a surface of the golf ball body, wherein thepaint film is composed of at least one layer, and an outermost paintfilm layer located at the outermost layer of the golf ball contains, asa base resin, a polyurethane obtained by a reaction between (A) apolyisocyanate composition and (B) a polyol composition, (A) thepolyisocyanate composition contains an adduct-modified product ofhexamethylene diisocyanate as a polyisocyanate component and thepolyisocyanate component contains the adduct-modified product ofhexamethylene diisocyanate in an amount of from 30 mass % to 100 mass %,the adduct-modified product of hexamethylene diisocyanate is a productobtained by a reaction between hexamethylene diisocyanate and apolyhydric alcohol, (B) the polyol composition contains a urethanepolyol as a polyol component, and the outermost paint film layer has adynamic friction coefficient of from 0.83 to 1.2 measured with a dynamicfriction tester under following conditions: <measurement conditions>moving speed: 2 mm/s load: 1.96 N measuring item: dynamic frictionaverage value in a moving distance of from 2 mm to 10 mm.
 2. The golfball according to claim 1, wherein the dynamic friction coefficient ofthe outermost paint film layer ranges from 0.83 to 1.1.
 3. The golf ballaccording to claim 1, wherein the urethane polyol has a weight averagemolecular weight in a range of from 5,000 to 20,000.
 4. The golf ballaccording to claim 1, wherein the urethane polyol includes a polyetherdiol as a constituent component.
 5. The golf ball according to claim 4,wherein the polyether diol has a number average molecular weight in arange of from 400 to 3,000.
 6. The golf ball according to claim 1,wherein the outermost paint film layer has a storage modulus (E′) in arange of from 10 MPa to 100 MPa at the temperature of 24° C.
 7. The golfball according to claim 1, wherein the outermost paint film layer has aloss modulus (E″) in a range of from 0.1 MPa to 80 MPa at thetemperature of 24° C.
 8. The golf ball according to claim 1, wherein theoutermost paint film layer has a 10% elastic modulus in a range of from1 kgf/cm² to 50 kgf/cm².
 9. The golf ball according to claim 1, whereina loss tangent (tan δ) of the outermost paint film layer measured with adynamic viscoelasticity measuring apparatus under following conditionshas a peak temperature in a range of from −40° C. to 40° C.:<measurement conditions> measuring mode: tensile mode measuringtemperature: −100° C. to 150° C. temperature increase rate: 4° C. /minoscillation frequency: 10 Hz measuring strain: 0.1%.
 10. The golf ballaccording to claim 1, wherein the adduct-modified product ofhexamethylene diisocyanate is combined with an isocyanurate-modifiedproduct, and a mass ratio (adduct-modified product of hexamethylenediisocyanate/isocyanurate-modified product) of the adduct-modifiedproduct of hexamethylene diisocyanate to the isocyanurate-modifiedproduct is 0.43 or more.
 11. The golf ball according to claim 10,wherein the adduct-modified product of the diisocyanate is anadduct-modified product of hexamethylene diisocyanate, theisocyanurate-modified product of the diisocyanate is anisocyanurate-modified product of hexamethylene diisocyanate, and thepolyisocyanate component contains the adduct-modified product ofhexamethylene diisocyanate and the isocyanurate-modified product ofhexamethylene diisocyanate in a total amount of from 70 mass % to 100mass %.
 12. The golf ball according to claim 1, wherein the paint filmhas a single layered structure.
 13. The golf ball according to claim 1,wherein the adduct-modified product of hexamethylene diisocyanate is atriisocyanate of formula (1) or formula (2) below:


14. The golf ball according to claim 10, wherein the adduct-modifiedproduct of hexamethylene diisocyanate is a product obtained by areaction between hexamethylene diisocyanate and a polyhydric alcohol.15. The golf ball according to claim 10, wherein the adduct-modifiedproduct of hexamethylene diisocyanate is a triisocyanate of formula (1)or formula (2) below:


16. The golf ball according to claim 10, wherein theisocyanurate-modified product is a compound of formula (3)


17. The golf ball according to claim 15, wherein theisocyanurate-modified product is a compound of formula (3)